OPINION
Following or during an arteriogram performed by a third-year radiology resident, plaintiff suffered a stroke which resulted in some permanent physical disabilities. Defendants appeal from a judgment entered after a non-jury trial which awarded damages of $120,000 to plaintiff, for “medical malpractice committed by agents and employees” of defendants. They raise four issues; however, their first two points require reversal, in our opinion, so we do not reach the additional arguments presented.
Plaintiff’s complaint alleged eight different theories of negligence: (1) Defendants failed to obtain prior medical reports and follow precautions that would have been evident from reading prior medical records, including the records of Mr. Camp’s admission at St. Joseph Hospital by Dr. Parsons in 1974 for repair of an abdominal aneurysm; (2) Defendants misdiagnosed bilateral femoral aneurysms; (3) Defendants performed a test that was potentially dangerous without adequate diagnosis and indication; (4) Defendants improperly administered a dangerous diagnostic test; (5) Even when the physician encountered resistance in trying to pass the catheter, the physician continued in his efforts to pass the catheter and further traumatized the artery; (6) There was failure on the part of the hospital personnel, including the doctors, to recognize and treat a cerebrovascular accident when it occurred; (7) Defendants proceeded with the diagnostic test in the absence of informed consent; (8) Dr. J. Davenport, the physician who performed the aortogram did not possess/use the knowledge and skill ordinarily known/used by a reasonably well qualified radiologist.
During the trial and over defendants’ objections, plaintiff was allowed to amend his pleadings to include allegations of “improper supervision or lack of supervision in not having a staff physician reasonably well *613qualified to participate in the decision" to have an arteriogram performed.
Prior to trial, counsel was asked by the trial judge whether Dr. Dobernick would be called because, as the judge later explained if Dobernick were to be a witness the judge felt he would have to recuse himself — the doctor was the judge’s next-door neighbor. Defense counsel responded that he had not intended to call that witness. At trial, however, and during the plaintiff’s examination of his last witness, a medical doctor, some evidence was adduced regarding the resident’s lack of expertise, particularly if not supervised, in performing an arteriogram. An objection was made on the ground that there was no evidence that the resident had not been supervised. The court responded:
Well, I don’t know that there’s any evidence to that. I assume you’re going to tie that up later. And if not, I’ll strike the answer. . . . [I]f there are no facts to establish the question, I’ll, of course, ignore it.
It was after the medical doctor completed his testimony, and after defendants had moved for dismissal for lack of evidence to support the allegations of the complaint, that plaintiff’s motion to amend the complaint was granted. Defendants’ objections that this introduced a new theory of negligence for which they had not had the opportunity to prepare, and that it was supported only by the opinion of plaintiff’s final witness “based solely on the absence of written notes in the [hospital] record,” did not persuade the trial court that the amendment should not be allowed.
Defendants thereupon advised the trial court that it would be necessary to call Dr. Dobernick as a defense witness on the issue of consultation and supervision. The request was refused.
Subsequently, a doctor who performed an examination of plaintiff four or five days before trial and was added as a witness, was permitted to testify beyond the boundaries the court imposed on her testimony when defendants objected to her being allowed to testify at all.
The trial court’s findings clearly reveal that plaintiff’s case was ultimately decided on the issue of lack of supervision and control — which was the negligence claim allowed by amendment after plaintiff had presented his evidence — and that the arteriogram would not have been ordered or performed if proper supervision and consultation had been obtained before the arteriogram was attempted. This state of facts presents the two issues determinative of this appeal, i. e., (1) Was it error to permit the trial amendment without also permitting defendants to call the judge’s neighbor as a necessary defense witness in refutation of the basis for the new claim of negligence? and (2) was defendant denied a fair trial when a last-minute medical witness was permitted to testify beyond a pre-trial limitation imposed by the court?
1. The trial amendment; the exclusion of essential testimony.
Amendments to pleadings are favored and should be liberally permitted in the furtherance of justice. Rule 15(b), N.M. R.Civ.P., N.M.S.A.1978; Martinez v. Research Park, Inc., 75 N.M. 672, 410 P.2d 200 (1965). However, when amendments to conform to the proof are asked, and there is no express or implied consent (as here), the test is whether prejudice would result to the opposing party if the amendment were allowed, i. e.,
whether [the defendant] had a fair opportunity to defend and whether he could offer any additional evidence if the case were to be retried on a different theory.
3 Moore’s Federal Practice 15-172, -173, ¶ 15.13[2]; see also Wynne v. Pino, 78 N.M. 520, 433 P.2d 499 (1967).
When the court refused to allow defendants to call Dr. Dobernick to meet the substance of the permitted amendment, it offered to accept a tender of proof. Plaintiff suggests that because defendants did not make a tender, any erroneous exclusion of evidence was cured or waived. N.M.R.Evid. 103, N.M.S.A.1978, requires a tender of evidence if a ruling excludes it, unless the substance of the evidence is clear to the *614judge by offer or is apparent from the context of the questioning. The necessity for Dr. Dobernick’s testimony was apparent from the moment defendants asked that he be allowed to testify on the supervision/consultation issue. Dobernick was the supervising physician from the Department of Surgery at the time the arteriogram was ordered. His testimony was crucial because plaintiff’s expert testified that lack of supervision or consultation in approving the arteriogram procedure would be negligence. The expert agreed, however, that merely because such a consultation was not written into the hospital records, the absence of a record was not conclusive that a consultation had not occurred: “That [documentation] isn’t [made] one hundred percent of the time.”
Nonetheless, the trial court permitted the trial amendment to allege negligence inherent in a lack of consultation or supervision, based on the expert’s assumption that failure to record a consultation indicated there had been none. The amendment added a new theory of negligence between the beginning and completion of plaintiff’s case. Plaintiff was granted the advantage of amendment, over strenuous defense objections; yet when defendants requested an adjustment to their pre-trial evaluation of defense witnesses to be called, in order that they might meet the new and unanticipated malpractice charge, the trial court refused to accord to them the same degree of liberality as was shown to plaintiff.
The prejudice to defendants in denying them the chance to adequately defend was sufficient to require refusal of plaintiff’s motion to amend. This is not a situation where a request for and allowance of a continuance would have helped; see 6 Wright and Miller, Federal Practice and Procedure: Civil 480-481, § 1495 (1971 ed.). Defense counsel had consulted with the medical director of the defendant hospital during the lunch hour, after plaintiff’s doctor had testified regarding lack of supervision, and had been assured that Dr. Dobernick would give evidence that he had been consulted regarding the proposed arteriogram. If the witness who had rendered the diagnostic consultation and supervision were not to be allowed to testify, a continuance would serve no purpose. Consequently, defendants were not required to seek one to preserve the error. Compare Batista v. Walter & Bernstein, 378 So.2d 1321 (Ct. App.Fla.1980); V. C. Edwards Contr. Co., Inc. v. Port of Tacoma, 83 Wash.2d 7, 514 P.2d 1381 (1973).
The court’s ruling on the amendment to the pleadings, together with its exclusion of essential defense evidence made necessary after the amendment was permitted, was an abuse of discretion. See Hambaugh v. Peoples, 75 N.M. 144, 401 P.2d 777 (1965). If defendants were to be bound by their preparatory assessment of necessary witnesses to defend against the pleaded act of negligence, so should plaintiff have been bound to the pre-trial acts of negligence alleged in his complaint against which the defense had had the opportunity to anticipate witnesses. Defendants were prejudiced, after the amendment was allowed, in presenting their defense upon the merits; N.M.R.Civ.P. 15(b), supra, condones amendments of the sort granted when such prejudice does not attach. The trial court should have granted the motion to amend and the request to call Dr. Dobernick, or it should have denied both.
2. Dr. Hollinger’s testimony.
Trial was set for Monday, May 5th. On the preceding Thursday defense counsel was advised by plaintiff’s counsel that a neurologist, Dr. Sonia Hollinger, had examined plaintiff on Wednesday (the day before) and would examine plaintiff’s medical records on Friday (the next day) to prepare “an updated evaluation of his [plaintiff’s] condition”; and that she “possibly” would be called by plaintiff as an expert witness. Defendants immediately sought a protective order and urged a continuance, contending extreme prejudice if Dr. Hollinger were to be added as a trial witness on such short notice — specifically, that defendants would be denied adequate opportunity to examine her before the trial. Counsel for *615plaintiff told the court that he intended to rely on Dr. Hollinger to establish plaintiff’s present medical condition, and he listed the conditions Dr. Hollinger had said she found on her Wednesday examination: residual hemiparesis, equilibrium problems and some memory loss. The court refused the continuance but ruled that if the doctor’s testimony was different during trial from his understanding that she would “be used just to state his present condition and was not going to testify as to the alleged act of malpractice . . . then I’ll grant your motion for continuance.”
We agree with defendants’ claim that plaintiff was allowed to far exceed the compass of Mr. Camp’s present physical condition in his questioning of the witness, and she in her replies. During and in response to defendants’ request for a ruling to limit testimony from Dr. Hollinger, the court again imposed this restraint on the questions and answers that would be permitted:
Well, as I indicated before, if you’re talking about any of the acts that led up to what they are claiming is the malpractice, .. . she cannot testify as to how those acts were performed or whether they were performed properly. I think we agreed to that.
If it’s just testimony about the condition afterwards and how that’s changed to date, I see no problem.
Subsequently, when asked to describe an arteriogram, the witness said, in part:
. . . The idea that they have in mind was to go down this way into the descending, so you could see both femorals here, the left and the right. It seems when they go around here, here in the upper part of the descending aorta, are the arteries who goes to the brain, to the right and to the left side of the brain.
He started with a common carotid that subdivides in the top into internal and external carotid.
And they went this way. They were trying to go down this way into the descending artery, but they could not. They struck the thing here, moving it back, who went up this way to the brain.
Defendants objected and asked that the testimony regarding the cause of the stroke be stricken; the court ruled it would not be stricken but, tacitly modifying its earlier ruling, said that “to the extent it’s an opinion and not borne out by the records, I’ll ignore it as far as establishing any kind of negligence.” Several more questions were asked, and eventually the following series of questions, objections, and answers ensued:
Q. Now, does that indicate to you— what does that indicate to you from the history of BCMC’s own doctor?
A. It seems to me, you know, that something [w]ent wrong.
(Objection — overruled).
Q. Well, let me ask it this way. Under primary and secondary diagnosis, it says, “Stroke, left internal capsulary thrombosis with dense right hemiparesis associated with an aortogram.”
A. Yes.
Q. What does that mean in plain language?
A. In plain language it means they did an arthrogram. And during the arthrogram, a stroke was made. And the only way that this can be done is—
(Lengthy objection, argument by both counsel; objection overruled).
And, finally,
Q. Now, then, Doctor, do you have an opinion as a matter of medical probability what caused — whether the stroke and right paralysis that Mr. Camp sustained was directly and proximately caused by the procedure of the arteriogram? (Objection — overruled).
A. Yes, I think it’s secondary to the arteriogram.
On all issues made by the pleadings in this case, defendants were entitled to depose every witness fully and exhaustively. Griego v. Grieco, 90 N.M. 174, 177, 561 P.2d 36 (Ct.App.1977), cert. denied, 90 N.M. 254, 561 P.2d 1347 (1977). “Such a right is basically fundamental to our system of jurisprudence and no court has power to restrict or limit it.” Griego, supra, citing *616 Northwestern University v. Crisp, 211 Ga. 636, 88 S.E.2d 26, 31 (1955). There is no question that Dr. Hollinger testified beyond the original limits proscribed by the court. She gave her opinion on ultimate issues of fact before the court. Plaintiff’s counsel insisted that he had represented she would testify about causation and the relationship of the arteriogram to the stroke, but the record does not bear him out on that contention; and the rulings of the court at trial were not in accordance with its ruling when the matter of Dr. Hollinger’s testimony was first brought to the court’s attention. Defendants should have been afforded the opportunity to discover the full extent of this witness’s testimony in order to adequately prepare to meet it; having reversed its earlier ruling during the presentation of this evidence, the court should have granted the continuance defendants were promised, so that defendants’ rights to a fair opportunity to defend and offer additional evidence, if available, would have been protected. See George M. Morris Const. Co. v. Four Seasons, 90 N.M. 654, 567 P.2d 965 (1977).
It is true that the granting or denying of a motion for a continuance rests in the discretion of the trial court and is not to be interfered with except for abuse. Tenorio v. Nolen, 80 N.M. 529, 458 P.2d 604 (Ct.App.1969). But Dr. Hollinger’s unexpected testimony required, in fairness and justice, that the discretion of the court be exercised favorably toward the continuance. We do not say that defendants will successfully defend when this case is retried, but we do hold that they are entitled to prepare for and conduct a defense free of eleventh-hour surprises.
This case is reversed and remanded for a new trial.
IT IS SO ORDERED.
ANDREWS, J., concurs.
SUTIN, J., dissents.